An international standardization project, 3GPP (3rd Generation Partnership Project) is discussing specifications of a network developed from W-CDMA (Wideband-Code Division Multiple Access) and GSM (Global System for Mobile Communications) as a mode of next-generation cellular mobile communication.
3GPP has been discussing cellular mobile communication systems for a long time and has standardized the W-CDMA as a third-generation cellular mobile communication system. HSDPA (High-Speed Downlink Packet Access) with higher communication speed has been standardized and the service is operated. 3GPP is currently also discussing development of the third-generation radio access technology (Long Term Evolution, hereinafter referred to as “LTE”) and LTE Advanced (hereinafter referred to as “LTE-A”) aimed at further increase in communication speed.
The OFDMA (Orthogonal Frequency Division Multiple Access) and the SC-FDMA (Single Carrier-Frequency Division Multiple Access) are using subcarriers orthogonal to each other to perform user-multiplexing and are discussed as communication schemes in LTE. Specifically, the OFDMA is a multi-carrier communication scheme and is proposed for downlink, and the SC-FDMA is a single-carrier communication scheme and is proposed for uplink.
On the other hand, for communication schemes in LTE-A, it is discussed to introduce the OFDMA for downlink and the Clustered-SC-FDMA (Clustered-Single Carrier-Frequency Division Multiple Access, also referred to as DFT-s-OFDM with Spectrum Division Control or DFT-precoded OFDM) for uplink in addition to the SC-FDMA. The SC-FDMA and the Clustered-SC-FDMA proposed as uplink communication schemes in LTE and LTE-A are characterized in that PAPR (Peak to Average Power Ratio) at the time of transmission of data (information) can be suppressed to a lower level.
While a typical mobile communication system uses a continuous frequency band, it is discussed for LTE-A to use a plurality of continuous/non-continuous frequency bands (hereinafter referred to as “carrier elements, carrier components (CC)” or “element carriers, component carriers (CC)”) in a composite manner to implement operation as one frequency band (wide frequency band) (frequency band aggregation, also referred to as spectrum aggregation, carrier aggregation, and frequency aggregation). It is also proposed to give different frequency bandwidths to a frequency band used for downlink communication and a frequency band used for uplink communication so that a base station apparatus and a mobile station apparatus more flexibly use a wider frequency band to perform communication (asymmetric frequency band aggregation: asymmetric carrier aggregation) (Nonpatent Literature 1).
FIG. 13 is a diagram for explaining frequency band aggregation in a conventional technique. Giving the same bandwidth to a frequency band used for downlink (DL) communication and a frequency band used for uplink (UL) communication as depicted in FIG. 13 is also referred to as symmetric frequency band aggregation (symmetric carrier aggregation). As depicted in FIG. 13, a base station apparatus and a mobile station apparatus use a plurality of component carriers that are continuous/non-continuous frequency bands in a composite manner, thereby performing communication in a wider frequency band made up of a plurality of component carriers. In this case, by way of example, it is depicted that a frequency band used for the downlink communication with a bandwidth of 100 MHz (hereinafter also referred to as a DL system band or a DL system bandwidth) is made up of five component carriers (DCC1: Downlink Component Carrier 1, DCC2, DCC3, DCC4, and DCC5) each having a bandwidth of 20 MHz. By way of example, it is also depicted that a frequency band used for the uplink communication with a bandwidth of 100 MHz (hereinafter also referred to as a UL system band or a UL system bandwidth) is made up of five component carriers (UCC1: Uplink Component Carrier 1, UCC2, UCC3, UCC4, and UCC5) each having a bandwidth of 20 MHz.
In FIG. 13, downlink channels such as a physical downlink control channel (hereinafter, PDCCH) and a physical downlink shared channel (hereinafter, PDSCH) are mapped on each of the downlink component carriers. And the base station apparatus uses the PDCCH to transmit to the mobile station apparatus the control information for transmitting a downlink transport block transmitted by using the PDSCH mapped on each of the downlink component carriers (such as resource allocation information, MCS (Modulation and Coding Scheme) information, and HARQ (Hybrid Automatic Repeat ReQuest) process information) (uses the PDCCH to allocate the PDSCH to the mobile station apparatus) and uses the PDSCH to transmit the downlink transport block to the mobile station apparatus.
The mobile station apparatus transmits the control information of HARQ (hereafter described as HARQ control information) on the basis of a codeword (CW, also referred to as code word). A CW is a bit sequence to which a transport block is mapped before channel encoding, and is a unit of channel encoding. The spatial multiplexing transmission in MIMO utilizes a plurality of CWs to generate transmission sequences. If the spatial multiplexing transmission in MIMO is performed, encoding is achieved with up to two CWs to generate transmission sequences. For example, in the spatial multiplexing transmission in MIMO, if the spatial multiplexing number (the number of layers) is two, spatial multiplexing sequences (layers) are encoded with respective different CWs to generate transmission sequences. If the number of layers is four, encoding is achieved with one CW per two layers to generate transmission sequences. Since transmission sequences are generated with a plurality of CWs in the spatial multiplexing transmission in MIMO in this way, the transmission sequences encoded with respective CWs have respective different transmission characteristics and, therefore, the HARQ control information must be transmitted for each transmission sequence encoded with each CW. Since the HARQ control information is transmitted for each CW of downlink signals (downlink transport blocks), two pieces of the HARQ control information are transmitted if the spatial multiplexing transmission in MIMO is performed, for example.
Uplink channels such as a physical uplink control channel (hereinafter, PUCCH) and a physical uplink shared channel (hereinafter, PUSCH) are mapped on each of the uplink component carriers. And the mobile station apparatus uses the PUCCH and/or the PUSCH mapped on each of the uplink component carriers to transmit to the base station apparatus the HARQ control information for the PDCCH and/or the downlink transport block. The HARQ control information is a signal (information) indicative of ACK/NACK (Positive Acknowledgement/Negative Acknowledgement, ACK signal or NACK signal) and/or a signal (information) indicative of DTX (Discontinuous Transmission) for the PDCCH and/or the downlink transport block. The DTX is a signal (information) indicating that the mobile station apparatus cannot detect the PDCCH from the base station apparatus. In FIG. 13, any of downlink/uplink channels such as the PDCCH, the PDSCH, the PUCCH, and the PUSCH may not be mapped on some downlink/uplink component carriers.
Similarly, FIG. 14 is a diagram for explaining asymmetric frequency band aggregation in a conventional technique. As depicted in FIG. 14, the base station apparatus and the mobile station apparatus give different bandwidths to a frequency band used for downlink communication and a frequency band used for uplink communication and use component carriers making up these frequency bands in a composite manner, thereby performing communication in a wider frequency band. In this case, by way of example, it is depicted that a frequency band used for the downlink communication with a bandwidth of 100 MHz is made up of five downlink component carriers (DCC1, DCC2, DCC3, DCC4, and DCC5) each having a bandwidth of 20 MHz, and that a frequency band used for the uplink communication with a bandwidth of 40 MHz is made up of two component carriers (UCC1 and UCC2) each having a bandwidth of 20 MHz. In FIG. 14, downlink/uplink channels are mapped on each of the downlink/uplink component carriers, and the base station apparatus uses the PDSCH allocated by the PDCCH to transmit the transport block to the mobile station apparatus and the mobile station apparatus uses the PUSCH and/or the PUSCH to transmit the HARQ control information to the base station apparatus.
To transmit the HARQ control information for transmission of PDCCHs and/or PDSCHs on a plurality of downlink component carriers, the mobile station apparatus must indicate ACK, NACK, and DTX for a PDCCH and/or a PDSCH transmitted on each of the component carriers. For example, if PDCCHs and/or PDSCHs are transmitted on five downlink component carriers, the mobile station apparatus needs to notify any one of ACK, NACK, and DTX and therefore must transmit information capable of indicating the fifth power of three types of state (243 types of state) to the base station apparatus.
To represent these types of state as bit information, eight bits (capable of representing 256 types of state) are required. If the spatial multiplexing transmission in MIMO is performed and transmission is executed with a plurality of CWs, ACK and NACK must be transmitted for each CW on each component carrier. For example, if a PDSCH is transmitted with two CWs applied in MIMO on one downlink component carrier, ACK and NACK must be represented for a first CW; ACK and NACK must be represented for a second CW; and DTX must be represented to indicate that no PDCCH is detected on the downlink component carrier; and, therefore, five types of state ((ACK, ACK), (ACK, NACK), (NACK, ACK), (NACK, NACK), (DTX, DTX)) must be indicated. In case that PDSCHs with spatial multiplexing in MIMO applied are transmitted on five downlink component carriers, if two CWs are applied to each of the component carriers, ACK and NACK for a first CW and ACK, NACK, and DTX for a second CW must be represented in each of the downlink component carriers and, therefore, the fifth power of five types of state (3125 types of state) must be indicated. To represent these types of state as bit information, 12 bits (capable of representing 4096 types of state) are required.
Nonpatent Literature 2 describes that, In case that a base station apparatus allocates two PUCCH resources to a mobile station apparatus and the mobile station apparatus respectively allocates PUCCH resources for different antennas to transmit different pieces of information through the respective antennas to the base station apparatus, more bit information (10-bit or more information) can be transmitted, and this transmission scheme can be applied to transmission of ACK/NACK to transmit ACK, NACK, and DTX described above.
Nonpatent Literature 3 proposes a transmission method in which a base station apparatus allocates to a mobile station apparatus a plurality of PUCCH resources for transmission of ACK and NACK such that the mobile station apparatus selects one PUCCH resource from the allocated PUCCH resources to transmit ACK and NACK to the base station apparatus by using the selected PUCCH resource. For example, the base station apparatus allocates to the mobile station apparatus the PUCCH resources corresponding to respective PDSCHs transmitted on a plurality of downlink component carriers and the mobile station apparatus selects one PUCCH resource from a plurality of the PUCCH resources to transmit ACK and NACK by using the selected PUCCH resource. The base station apparatus extracts the PUCCH resource selected by the mobile station apparatus in addition to bit information transmitted by the mobile station apparatus, thereby enabling the base station apparatus and the mobile station apparatus to transmit/receive more information indicative of ACK and NACK.